The Mental Healthcare Act, 2017 was enacted in pursuance of India’s obligations under the United Nations Convention on the Rights of Persons with Disabilities. The Act seeks to regulate mental health care and treatment through a rights-based approach while protecting decisional autonomy. It brings forth a significant shift in the law on decisional capacity for persons with mental illness with respect to: (i) admissions in mental health establishments; (ii) access to support for exercising decisional capacity for mental health care and treatment decisions; and (iii) providing informed consent for treatment and care options in accordance with one’s will and preferences. Additionally, emerging constitutional jurisprudence on decisional autonomy and privacy in India has significant implications for enabling the decisional capacity of persons with mental illness under the Act. In this light, this chapter will examine how the Act’s provisions and emerging rights jurisprudence seek to protect decisional autonomy as a fundamental right under India’s Constitution.